Sforno on Numbers 32:6/ספורנו על במדבר ל״ב:ו׳

1?האחיכם יבאו למלחמה; Did you really think that your brethren are going to war in order to make conquests

2?ואתם תשבו פה, while you are settled here on land that we have already conquered? Surely you did not think for a moment that you could get away with such an arrangement! Your suggestion therefore can only have the effect of undermining the morale of your brethren!